1. Field of the Invention:
The present invention relates to a keyboard for use as an input device for various information processing equipments such as personal computers and word processors.
2. Description of the Related Art:
A conventional keyboard is disclosed in Japanese Utility Model Application No. 60-185509 applied for on Dec. 3, 1985 for utility model registration by the present applicant. That Japanese application was published on June 16, 1987 as a kokai 62-94520.--; This keyboard will be described with reference to FIGS. 1 through 5.
Referring to FIG. 1 showing a keyboard in a schematic side elevation, the keyboard comprises keys 1, a key holding frame 2, a base plate 3 provided with contact circuits, a bottom plate 4 formed of a metal plate having large rigidity, and a casing 5 indicated by alternate long and two short dashes lines. Referring to FIGS. 2 and 3, the key holding frame 2 is an integral member having a plurality of housings 2a respectively for receiving the keys 1 therein, a plurality of hooks 2b, and two posts 2c. The base plate 3 has a plurality of rectangular holes 3a respectively for receiving the hooks 2b of the key holding frame 2 therethrough, and two circular holes 3b respectively for receiving the posts 2c to position the key holding frame 2 relative to the base plate 3. The bottom plate 4 has a plurality of rectangular holes 4a with which the hooks 2b of the key holding frame 2 engage, respectively, to define the vertical position of the key holding frame 2 relative to the bottom plate 4 and two circular holes 4b for receiving the post 2c of the key holding frame 2 to position the key holding frame 2 relative to the bottom plate 4.
In assembling the keyboard, the bottom plate 4, the base plate 3 and the key holding frame 2 are placed one over another in that order with the two posts 2c of the key holding frame 2 positioned opposite to the two circular holes 3b of the base plate 3 and the two circular holes 4b of the bottom plate 4, respectively. Then, as shown in FIG. 4, the key holding frame 2 is pressed in the direction of an arrow B so that the inclined surface 2d of the head 2f of each hook 2b of the key holding frame 2 slides along one side 4c of the corresponding rectangular hole 4a of the bottom plate 4, and thereby the leg 2e of each hook 2b is forced to flex and the head 2f of the hook 2b projects downward from the rectangular hole 4a of the bottom plate 4 and engages the edge of the corresponding rectangular hole 4a. In this state, the respective legs 2e of the hooks 2b are flexed resiliently so as to strain each other, so that the heads 2f of the hooks 2b firmly engage the respective side edges of the corresponding rectangular holes 4a to join the key holding frame 2, the base plate 3 and the bottom plate 4 firmly together. The relative position between the key holding frame 2, the base plate 3 and the bottom plate 4 is determined by the engagement of the posts 2c and the circular holes 3b and 4b. The base plate 3 and the bottom plate 4 may be formed integrally in a single member.
This keyboard, however, requires a large force to press the key holding frame 2 in the direction of the arrow B in assembling the key holding frame 2, the base plate 3 and the bottom plate 4 making the assembling work difficult and, in some cases, the key holding frame 2, the base plate 3 and the bottom plate 4 cannot firmly be joined together owing to the plastic deformation of the tips 2g of the hooks 2b as shown in FIG. 5. Furthermore, since the longitudinal and lateral movement of the base plate 3 relative to the key holding plate 2 is limited by the engagement of the posts 2c and the circular holes 3c, the central portion of the key holding frame 2 is caused to warp particularly with respect to the longitudinal direction by the difference in coefficients of thermal expansion between the key holding frame 2 and the base plate 3, which makes the keys give an unpleasant touch or feel to the fingers when in use.